The present invention relates generally to the field of balancing technology. More specifically, the invention incorporates a dual-position drive member into a dynamic balancing machine for imparting rotational forces to a rotating workpiece during dynamic balancing operations involving the workpiece. In dynamic balancing operations, a workpiece is usually rotated at high speeds. Sensors mounted on or attached proximate the bearing points of the workpiece detect any vibrational forces and transmit a signal to a processor, the signal being used to determine the amount and location of any unbalance in the rotating mass of the workpiece.
A machine used in the dynamic balancing of a workpiece usually includes a base having a cradle system for supporting the workpiece during the balancing operation. The base and cradle members are constructed of a substantial enough mass that external vibrational forces encountered by the base and cradle system are sufficiently damped to eliminate unwanted interference while sensing vibrational imbalance in the rotating workpiece. The sensors utilized for locating the unbalance in the workpiece are generally provided in combination with highly sensitive resilient mounts on the cradle members. Since the base and cradle system are relatively stable, the sensors are intended to primarily receive vibrational input from the unbalance in the workpiece. However, the drive system used to impart the rotational forces to the workpiece during the balancing operations remains the only balancing machine structure in dynamic contact with the workpiece during the critical measuring step of the balancing operation. If the drive system has some imbalance, the accuracy of the unbalance measurements taken by the sensors may adversely affected.
There are several important functions for which it is necessary to account, when designing the drive system for a dynamic balancing machine. The drive system must be able to apply the rotational forces to the workpiece, usually through contact friction, in order to accelerate the workpiece to an acceptable balancing speed. The drive system must also be able to maintain the rotation of the workpiece at a steady-state speed throughout the time required for the sensors to measure the vibrational forces and detect the amount and angle of unbalance. The drive system must also be able to rapidly decelerate the workpiece to a stop. Finally, when used in an automatic or semi-automatic balancing operation, the drive system must also be able to accurately and rapidly index the workpiece to a predetermined position for the correction procedure.
Since the drive system maintains contact with the workpiece throughout the balancing operation, any vibration developed in the drive system or in the engagement between the drive system and the workpiece will be transmitted through the workpiece to the sensors. Since this drive system-induced vibration is not a true component of the workpiece unbalance forces being measured by the sensors, the drive system-induced vibration jeopardizes the accuracy and resolution of the unbalance readings. This drive system vibration cannot be easily taken into account through electronic signal manipulation as it does not remain constant. Deterioration and wear of the drive system components, such as belt deterioration and bearing wear, greatly affects the repeatability in the unbalance measurement operations. Therefore, it is imperative to reduce as much as possible the influence of any drive system vibration on the unbalance measuring step in dynamic balancing operations.
It has been found that the drive system-induced vibration can be reduced by either decreasing the contact area between the drive system and the workpiece or decreasing the forces applied to the workpiece by the drive system. However, the reduction in drive-induced vibration achieved by these methods is usually offset by a loss of workpiece processing speed due to the creation of longer acceleration and deceleration times as well as a real loss of accuracy in indexing the workpiece for correction.
Other attempts to reduce the impact of drive-system-induced vibration on the unbalance measuring step have resulted in machine designs wherein the workpiece is accelerated by a drive belt or wheel to a desired rotational speed, at which point the drive wheel or belt is completedly disengaged from the rotating workpiece. The unbalance measurement is then taken on the coasting workpiece. While such a machine is effective in given balancing operations, there are a plethora of appications and workpieces where a continuous drive is demanded to maintain the rotational speed of the workpiece at a steady-state during the unbalance measuring step. The unbalance measuring step may last as long as four to six seconds and the rotational speed of a coasting workpiece can slow considerably over that interval.
The present invention is directed toward achieving a steady-state rotational speed and a reduction in the drive system-induced vibration during the measurement portion of the balancing cycle while maintaining an acceptable processing standard for acceleration and deceleration times as well as maintaining the indexing accuracy in automatic and semi-automatic balancing systems.